The networking of control devices, sensors and actuators with the aid of a communications system, i.e., a bus system, has drastically increased in recent years in the construction of modern motor vehicles. Synergy effects due to the distribution of functions among multiple control units or sensors and actuators may thereby be obtained. In this context, one speaks of “distributed systems”. Communication between the different users in such distributed systems is taking place more and more via a bus, or rather a bus system. The communications traffic on the bus system, access mechanisms and receiving mechanisms as well as error handling are governed via a protocol.
Future door architectures provide for a networked structure of all electrical components found in it. The lock, mirror, power window unit and operating element, etc. are connected to a bus system and controlled by a central control device or a central control unit. A bus system of this sort includes a data line on which data are exchanged bidirectionally between the connected users.
One example of such a bus system is the LIN (local interconnect network), a master/slave bus whose users are connected via a logical bus line. A maximum of one master and up to 64 slaves belong to each bus. An unshielded physical single-wire line is used as the transmission medium. The LIN protocol divides the transmit and receive process into two tasks. The master task contains the synchronization and addressing, and the slave task contains the data. Both—master task and slave task—are combined in a so-called message frame. A master is able to carry out the master task as well as the slave task. Each data transmission is made up of a message frame in which both the synchronization information and the data information are transmitted. At the start of each message, the master sends a synchronization interruption in the master task, known as a “SynchBreak”, in order to fetch the slaves out of a possible idle state and to enable synchronization. Subsequently, this is then followed by pure synchronization information as well as an identifier which uniquely describes the data content of each message frame and also, encoded, reflects the length of the subsequent data.
Like the cited example of the LIN bus, there are a number of bus systems which may be used as a communications link between corresponding users, particularly in these distributed systems in door architectures. In this context, prevention of unauthorized access to these systems is gaining increasing importance. In today's bus systems in motor vehicles, a large part of the data is transmitted unprotected. If the bus line is connected to an unauthorized user, he can send commands that trigger, for example, the unlocking of the central locking system or other closure systems and thus unlocking of the vehicle. A major problem related to break-in prevention is thus that the potential for external energizing of the closure system or the locking system or parts thereof from outside, thus outside of the lockable vehicle interior, is enabled because bus users are arranged outside of this lockable vehicle interior, and opening of the vehicle is enabled via them, i.e. the connecting lines leading there. Locking system or closure system is used to mean all parts that prevent penetration into the passenger compartment or the vehicle area (interior, trunk). Besides locks, this also includes power window units and the associated locking mechanisms, etc.